1. Field of the Invention
The present invention is directed to circuit-board-processing lines and in particular to controlling their operation.
2. Background Information
Circuit-board manufacture typically involves using a sequence of disparate machinery to perform successive operations on the same circuit boards. A board-processing line may include machines for depositing solder paste onto the boards, for placing components on them, for performing visual inspections of the boards thus populated by components, for causing solder to reflow and thereby establish electrical connections among the components, and for performing electrical tests on the resultant boards. It is desirable, of course, for all of these and other types of circuit-board-processing machines to cooperate in such a manner as to make the overall assembly process as automatic and efficient as possible. But overall control is complicated by the fact that different machines on the same line will typically have been made by different manufacturers. The capabilities for automatic control that the different line-machinery manufacturers provide tend not to have been selected with a common overall-control scheme in mind.
True, manufacturers have arrived at some standardization for rudimentary communication between successive machines so that they can xe2x80x9cknowxe2x80x9d when the previous machine is ready to supply a new board and when the next machine is ready to receive one. The Surface Mount Equipment Manufacturers Association (xe2x80x9cSMEMAxe2x80x9d) Interface Standard specifies the physical arrangement of an electrical interface between successive circuit-board-processing machinery and further specifies the meaning to be assigned to different states of that interface. (We note at this point that, although the first two letters in SMEMA stand for xe2x80x9csurface mount,xe2x80x9d the SMEMA standard""s adoption has not been limited to machines that handle boards populated with surface-mount components.)
For an upstream machine to inform the downstream machine that the upstream machine is ready to supply another board, for instance, the SMEMA standard specifies that the upstream machine should send a xe2x80x9cboard availablexe2x80x9d signal by shorting together two specified conductors in the SMEMA interface. And, to determine whether the downstream device is ready to receive the next board, the upstream device senses whether the downstream device has sent a xe2x80x9cmachine readyxe2x80x9d signal by shorting together two other specified conductors. By conforming to this standard, circuit-board-processing machinery from different manufacturers can to an extent coordinate workflow along a manufacturing line.
But providing a higher level of control is more complex. For example, an inspection station at one point along the line may detect defects to which a high-level line-coordination system might best respond to by affecting the operation of, say, a pick-and-place machine located several positions upstream of the inspection station. But that pick-and-place machine may not provide an appropriate electrical interface by which it can be commanded to respond in the desired fashion. So the board manufacturer is forced either to make custom modifications to its machines so that they have the needed capabilities or to do without as great a degree of higher-level control as would be preferable.
We have recognized, though, that a significant amount of the additional desired capability can be provided by interposing in the SMEMA channel between successive machines a SMEMA-device emulator, i.e., an apparatus that receives and transmits the SMEMA signals without necessarily performing any associated board processing. That is, a SMEMA-device emulator will typically send and receive the SMEMA-defined xe2x80x9cboard-availablexe2x80x9d and xe2x80x9cmachine-readyxe2x80x9d signals without actually presenting a circuit board or having a state in which it can in some sense process one. But such emulators appear as the upstream and downstream machines to the downstream and upstream machines, respectively, so that, say, the downstream circuit-board-processing machine can be sent a signal different from the signal that the upstream circuit-board-processing machine is actually sending.
Such emulators, often referred to as xe2x80x9cbreak-out boxes,xe2x80x9d have frequently been used in the past for manual intervention in circuit-board-processing lines. But we provide the emulators with ports for non-SMEMA communications channels by which communication with coordination circuitry can occur. The coordination circuitry can thereby use an emulator to control the SMEMA-channel signals in response to signals that the coordination circuitry receives from other line machinery or from one or more other SMEMA-device emulators. The coordination circuitry can also control line machinery in response to SMEMA-channel signals that an emulator has sensed and reported to it over the non-SMEMA communications channel. As will be explained by example below, this provides ways of expanding a board-processing line""s control capabilities without making custom modifications to the line""s component machines.